Applications of the rotating photobioreactor

Abstract

A method to recover and harvest nutrients and volatile gases such as alcohols from a liquid stream using a fixed film bioreactor. The method includes a means of concentrating product gas stripped from a bioreactor.

I claim: 
     
       1. A process for recovering volatile and non-volatile products from a substrate-laden influent stream using microorganisms growing in a rotating bioreactor contactor, said bioreactor including a vessel, a shaft mounted for rotation within said vessel about a shaft axis, a plurality of axially spaced-apart, growth plates attached to the shaft, each of the plates having surfaces to which a fixed film of the microorganisms are attached, and means for rotating the shaft and plates about the axis, comprising the simultaneous steps of:
 (a) operating the rotating bioreactor as an aerobic, facultative or anaerobic reactor; 
 (b) feeding the influent stream past the growth plates such that the growth plates are partially submerged within the stream, whereby, as they grow, the microorganisms convert the substrate to volatile products and accumulate biomass; and 
 (c) passing a stripping gas past the growth plates to harvest the volatile products as stripped gas. 
 
     
     
       2. The process of  claim 1 , wherein the microorganisms include heterotrophic microorganisms capable of converting the substrate into alcohols whereby the stripped gas includes butanol or other linear or branched chain alcohols. 
     
     
       3. The process of  claim 2 , wherein the microorganisms include  Clostridium acetobutylicum.    
     
     
       4. The process according to  claim 2 , further comprising inserting the stripped gas into a condenser cooled by a chiller and operating at a temperature less than the temperature of the liquid in the vessel, whereby the stripped gas and water vapor are condensed to form a condensate product and a gas that is deficient in said product. 
     
     
       5. The process of  claim 4 , further comprising recirculating the gas that is deficient in said product past the growth plates for further stripping. 
     
     
       6. The process of  claim 5 , wherein if the temperature of the gas that is deficient in said product is less than the temperature of the liquid in the vessel, further comprising heating said gas up to said temperature and recirculating said heated gas past the growth plates for further stripping. 
     
     
       7. The process of  claim 5 , further comprising discharging excess stripping gas and/or providing make up stripping gas through a pressure and vacuum relief valve. 
     
     
       8. The process according to  claim 5 , wherein the stripping gas includes one or more of air, methane, nitrogen and/or oxygen, comprising further concentrating the product by the steps of:
 (a) conveying the stripped gas to an upstream side of a membrane disposed within a plenum, said membrane having a high permeability rate for water and a lower permeability rate for the stripping gas, and said stripping gas stream comprising stripping gas, water vapor, and stripped gas; 
 (b) applying a differential pressure between the upstream side of the membrane and an opposite downstream side of the membrane, whereby water vapor passes through the membrane to the downstream side of the membrane as water vapor permeate, and the gas on the upstream side of the membrane becomes depleted of water vapor as retentate gas; and 
 (c) combining the water vapor permeate formed in step (b) with the retentate gas that is deficient in condensate product to form a combined stripping gas. 
 
     
     
       9. The method of  claim 1 , wherein a gas is introduced into the rotating bioreactor contactor above the influent stream to increase the growth rate of said microorganisms. 
     
     
       10. The method of  claim 9 , wherein the rotating bioreactor contact has been converted into a rotating photobioreactor by equipping the rotating bioreactor contactor with a light source directed at the microorganisms, said microorganisms include autotrophic microorganisms, and said introduced gas comprises carbon dioxide. 
     
     
       11. The method of  claim 9 , wherein said microorganisms include heterotrophic microorganisms and said introduced gas comprises oxygen. 
     
     
       12. A process for concentrating the chemical constituents of a stripping gas stream, regardless of the source of the stripping gas stream, using a membrane disposed within a plenum, said membrane having an upstream side and an opposite downstream side, said stream including stripping gases, water vapor, and stripped product gas, wherein said stripped product gas includes ammonia and/or volatile biomass fermentation products including butanol and other alcohols, comprising the steps of:
 (a) conveying the stripping gas stream to the upstream side of the membrane, said membrane having a high permeability rate for water and a lower permeability rate for the stripping gas; 
 (b) applying a differential pressure between the upstream side of the membrane and the downstream side of the membrane, whereby water vapor passes through the membrane to the downstream side of the membrane as water vapor permeate, and the gas on the upstream side of the membrane becomes depleted of water vapor as retentate gas; 
 (c) condensing the retentate gas formed in step (b) in a condenser to form condensate product and retentate gas that is deficient in said condensate product; and 
 (d) combining the water vapor permeate formed in step (b) with the retentate gas that is deficient in condensate product to form a combined stripping gas. 
 
     
     
       13. The process of  claim 12 , further comprising passing the combined stripping gas past the growth plates of a rotating photobioreactor, said rotating photobioreactor including a vessel, a shaft mounted for rotation within said vessel about a shaft axis, a plurality of axially spaced-apart, growth plates attached to the shaft, each of the plates having surfaces to which a fixed film of the microorganisms are attached, means for rotating the shaft and plates about the axis at a user-selectable rotational speed, and illumination means, while simultaneously performing the steps of:
 (a) shining light upon the microorganisms with the illumination means; 
 (b) optionally feeding a carbon source into the vessel; and 
 (c) feeding the influent stream past the growth plates such that the growth plates are partially submerged within the stream, whereby, as they grow, the microorganisms remove nutrients from the influent stream, capture the nutrients in biomass, emit oxygen gas, and convert the influent stream to a nutrient-deficient effluent stream; and 
 
       further comprising
 (d) using the harvesting means to remove a portion of the microorganisms from the surfaces of the growth plates. 
 
     
     
       14. The process of  claim 13 , further comprising passing the combined stripping gas through a heater to raise the temperature thereof up to the temperature of the liquid in the vessel, and then passing the heated, combined stripping gas past the growth plates. 
     
     
       15. The process according to  claim 13 , wherein the differential pressure across the membrane is maintained by a recirculating blower and control valve to cause the return flow of water vapor permeate with its latent heat to the rotating photobioreactor. 
     
     
       16. The process according to  claim 12  or  13  wherein the condensate product comprises aqua ammonia concentrated to 10 percent (w/w) or more, suitable for use in the pretreatment of lignocellulosic biomass for renewable energy production. 
     
     
       17. The process according to  claim 12 ,  13  or  14 , wherein the condensate product comprises a highly concentrated aqua ammonia concentrated to 20 percent (w/w) or more, suitable for use as diesel exhaust fluid. 
     
     
       18. The process of  claim 14 , wherein the differential pressure across the membrane is maintained by a recirculating blower and control valve to cause the return flow of water vapor permeate with its latent heat to the rotating photobioreactor.